The longterm goal of our research program is to elucidate the complex neural processing of chemical and mechanical respiratory afferent inputs that underlie the control of breathing by brainstem nuclei in health and in cardiopulmonary diseases. In the past project period we have used single-electrode, single-unit recording and central microinjection and lesioning techniques to explore the neuronal structures and functions in the dorsolateral pons pneumotaxic center and the dorsomedullary nucleus tractus solitarius (NTS) which participate importantly in the integration of vagal and chemoreceptor afferent inputs. In the next phase of our research we propose to employ a state-of-the-art multielectrode/multineuronal recording technique in order to characterize these pontomedullary nuclei at the neural networks level. Our experimental approach combines advanced multielectrode/multineuronal recording technology which is miniaturized for application in the rat brainstem, and advanced statistical techniques for ensemble spike train analysis and data mining in order to decipher the connectivity of the recorded neurons. A key question to be addressed in this project is whether central and peripheral chemoreceptor inputs are simply relayed by pontine respiratory neurons to the respiratory controller or are integrated in a specific manner in modulating the ventilatory pattern. Our specific aims are to identify and characterize the neural correlates of hypoxic-hypercapnic ventilatory interaction in four major pontine nuclei (Aims 1-4): Lateral and medial parabrachial nuclei and K"lliker-Fuse nucleus in the dorsolateral pons and the A5 region in the ventrolateral pons. Our hypothesis is that a subset of pontine respiratory neurons may integrate hypoxic and hypercapnic inputs in modulating respiratory drive and respiratory rhythm, such that the individual neuronal response and the overall phrenic nerve response to a combination of these inputs may be greater (positive interaction) or smaller (negative interaction) than the sum of responses to separate inputs (no interaction). Identification of the neural correlates of hypoxic-hypercapnic ventilatory interaction and resultant modulation of respiratory drive and respiratory rhythm will shed light on the mechanisms of respiratory instability in certain at-risk subject populations, such as congestive heart failure patients and individuals sleeping at high altitude. PUBLIC HEALTH RELEVANCE: Breathing is a vital bodily function that is fundamental to life. Understanding how various brainstem centers integrate afferent information in the control of breathing is of fundamental importance in the clinical management of a variety of life-threatening conditions such as respiratory failure, chronic cardiopulmonary or airway diseases, sleep apnea, or exposure to extreme environments such as high altitude.